The mating system of the Marine Iguana (Amblyrhynchus cristatus)
Zeitschrift für Tierpsychologie
1983
Journal Article
63
2-3
141-172
Amblyrhynchus cristatus
The mating system of marine iguanas (Amblyrhynchus cristatus) was studied on Caamaño islet with the aim of understanding how gregariousness of females and their behaviour influence the degree of polygyny attainable by males; the costs and benefits of territorial behaviour and feeding pattern of territorial males were estimated by their influence on body condition and mating success. The mating readiness of females was well synchronized to only 24 days in Jan. Females moved daily to the intertidal zone to forage and showed high fidelity to their resting sites. Males defended territories in the colony and not individual females. Two types of territory existed: resting‐territories where females stayed during high tide and overnight, and transit‐territories through which females passed on their way to and from foraging areas. Territoriality of males began at the end of Oct., immigrant males from Santa Cruz arrived about one month later and evicted a few of the resident males. Males stayed on their territories until the end of Jan. when the territory system broke down rapidly. During the reproductive period males shortened their foraging time and even fasted for some time in Jan. (median fast duration 12 days). They lost up to 26% body weight during this period and recovered from this weight loss only shortly before the next reproductive season. Long term records (max. six consecutive seasons) of a few males suggest that males slowly lose weight over several seasons. Weight loss of males within a season correlated significantly with their early‐season weight, fasting period duration and number of copulations achieved. Courtship and copulation are described. Females normally copulated only once and only with territorial males. Breeding success of territorial males varied considerably, from 0 to 45 copulations within one season. Territory area, early‐season weight of the owner and number of females on a territory correlated significantly with the number of copulations achieved. Territory quality is shown greatly to influence mating success of males. Other factors influencing breeding success and the cost of breeding are discussed and evidence against female mate choice is given. The convergence of the marine iguanas' mating system to that of pinnipeds in territorial spacing of males, variability of males' breeding success and selection for sexual size dimorphism is pointed out. Gregariousness of females has evolved under different selection pressures in the two groups and pre-adaptations for prolonged territory maintenance are shown to differ substantially in accordance with the different physiology of reptiles and mammals.